Spectrophotometers operable for performing enzyme-linked immunosorbent assays (ELISA) are widely known and used in the pharmaceutical and biotechnology industries. Of special interest are such spectrophotometers adapted for performing a kinetic analysis of the rate of change of optical density (OD) within a sample. Typically a plurality of samples are provided within a plurality of wells formed within a plate, also known as a microplate. A source of radiation is provided for illuminating one or more of the wells and the transmission of radiation through each of the samples is repetitively measured, the amount of transmission being indicative of the OD of the sample. The OD is in turn indicative of the enzyme activity of the sample.
One consideration with such kinetic analysis spectrophotometers is the speed at which each of the sample wells within a microplate is measured. In that an initially linear OD excursion may occur in a relatively short period of time, a sufficient number of readings must be acquired rapidly in order to characterize the slope of the reaction. The individual sample acquisition rate also directly influences the amount of time required to read an entire microplate, which may contain 96 sample wells arranged in a two dimensional array. In that several dozen or even hundreds of microplates may be required to be sequentially read by the spectrophotometer, the amount of time required to acquire data from a single plate is of importance.
Another consideration is the consistency of measurement accuracy of wells on the same plate in that certain of the wells may contain a reference sample against which other wells are measured. Measurement consistency is a function at least of the uniformity of the illumination from well to well.